1) Field of the Invention
The invention relates to a method for the electron-microscopic observation of a semiconductor arrangement having a topology with a high aspect ratio. The invention further relates to an apparatus for observing such a semiconductor arrangement.
2) Brief Description of Related Art
Structures with a high aspect ratio are usually encountered in semiconductor manufacture. These are, for example, contact holes, trenches, etc.
In order to image semiconductor structures and, in particular, in order to visualize defects in such semiconductor structures during manufacture, electron-microscopic methods are conventionally employed.
A very common method in this respect is to image semiconductor structures by means of a scanning electron microscope “SEM”. However, it has been found that it is difficult to image structures with a high aspect ratio by means of a SEM, because secondary electrons which emanate from bottoms of deeper regions of the structures are absorbed by the walls of such structures. As a result, a significant number of such secondary electrons cannot enter the objective of the microscope. Therefore, deeper structures cannot be satisfactorily imaged by means of a SEM.
From U.S. Pat. No. 6,232,787 B1, a method is known wherein a SEM is used to negatively charge upper surfaces of a semiconductor structure to be examined relative to a bottom of a recess which has a high aspect ratio and is surrounded by the upper surface. Due to this charging, artifacts are deliberately generated in the imaging of the semiconductor structure. It can thus be concluded from these artifacts the presence of manufacturing defects of the structure with a high aspect ratio, for example, a hole. This is because the artifacts cause a hole fabricated with a defect to appear in the electron-microscopy image larger or smaller than a hole corresponding to the specification. However, in this respect, it is presumed that each hole has a predetermined hole size which is then compared with the hole size appearing in the electron-microscopic image. However, this method does not provide a satisfactory image of the hole bottom either.